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Introduction to Parasites

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Define parasite
Organism which lives on or in another organism at whose expense the parasite gains some advantage
What is the importance of parasitic diseases for human health from a global perspective
Parasitic diseases are very prevalent on a global basis, especially in developing countries. Have an important worldwide impact on morbidity and mortality
Why are life cycles of parasites geographically related
Geographic distribution is related to type of host that parasite requires. Taking a good travel hx for a patient may help you find out if they have a parasite.

Ex. Protozoa that causes malaria specifically infects mosquito that only lives in certain area
What are Helminths?
Metazoans (parasitic worms that infect humans)

Roundworms/Nematodes, Flatworms/Trematodes/Flukes
Tapeworms/Cestodes
What are Protozoas
Unicellular eukaryotic parasites that infect humans

Amoebas
Flagellates
Ciliates
Sporozoa
Microsporidia
Schistosomiasis
Flatworm transmitted to humans in fresh contaminated water.

Eggs shed in feces or urine
Hatch in fresh water
Develop into cercaria in snails
Penetrate human skin (dermatitis)
Migrate to portal blood/mesenteric veins/venous plexus and mate (serum sickness like illness 4-8 weeks after skin invasion can see lymphadenopathy and hepatosplenomegaly)
Eggs produced and circulate in venous blood through liver
Released to intestines/bladder to expel and infect more hosts


Chronic disease you see granulomatous/fibrotic changes in the liver/bladder due to eosinophils and reaction to deposited eggs
Malaria
Infected mosquitoes bite humans
Inject sprozoites
Replication in liver
Merozoites released and infect erythrocytes
Asexual replication
Lysis and release of merozoites (illness like fever and periodic symptos of anemia, hemaglobinuria)

Pt are jaundiced hypotensive have hepatosplenomegaly and tachycardia with fever. Can have complications like cerebral malaria, immune complex deposition in glomerulus
Challenges to preventing parasitic diseases?
Widespread, large and impossible to eradicate (for example, all mosquitos)

DDT used but can gain resistance and has bad side effects

Antimalarials (doxycycline, mefloquine)
Public Health strategies for controlling schistosomiasis
building wells/latrines, providing potable water, preventing contamination of environmental water, education about disease, use of molluscides to control snail hosts and treatment with drugs like praziquantel. Vaccination?